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Section 15.1 Summary – pages Structural adaptations arise over time  The ancestors of today’s common mole-rats probably resembled African rock rats.  Learning about adaptations in mole-rats can help you understand how natural selection has affected them.

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Section 15.1 Summary – pages Structural adaptations arise over time  Some ancestral rats may have avoided predators better than others because of variations such as the size of teeth and claws.

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Section 15.1 Summary – pages Structural adaptations arise over time  Ancestral rats that survived passed their variations to offspring.  After many generations, most of the population’s individuals would have these adaptations.

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Section 15.1 Summary – pages Structural adaptations arise over time  Over time, natural selection produced modern mole-rats.  Their blindness may have evolved because vision had no survival advantage for them.

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Section 15.1 Summary – pages  In another form of mimicry, two or more harmful species resemble each other.  For example, yellow jacket hornets, honeybees, and many other species of wasps all have harmful stings and similar coloration and behavior. Structural adaptations arise over time

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Section 15.1 Summary – pages  In another form of mimicry, two or more harmful species resemble each other.  For example, yellow jacket hornets, honeybees, and many other species of wasps all have harmful stings and similar coloration and behavior. Structural adaptations arise over time

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Why Evolution Is Not Perfect 1. Natural selection only edits variations that already exist in a population. Evolution has to make do with what is created; the new designs, although better than the old ones, are less than perfect. 2. Adaptations are often compromises of what an organism is ideally aiming to achieve. 3. Not all evolution is adaptive. Sometimes chance events can change the composition of a populations gene pool. Those organisms which survive a chance events do so randomly, not because they were better than other organisms.  The individuals that do survive are able to reproduce and pass on their genes to their offspring. Over time the population will change, hopefully for the better.

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Adaptive Radiation I  The diversification of a common ancestral species into a variety of species is called adaptive radiation.  Darwin’s finches are a good example of adaptive radiation.  The first inhabited a single island. Eventually, the finches began to inhabit other neighboring islands. These islands had slightly different environments from each other and the selective pressures of the different environments resulted in different feeding habits and morphological differences for the finches.

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Darwin’s Finches & Adaptive Radiation

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Adaptive Radiation II  Islands are a great environment for studying speciation because they give organisms the opportunity to change in response to new environmental conditions.  Each island has different physical characteristics which help the process of adaptive radiation to occur.  Adaptive radiation can also occur after mass extinction events in the Earth’s history.

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Divergent & Convergent Evolution  Divergent evolution Pattern of evolution in which species that were once similar diverge or become increasingly different from each other Divergent evolution occurs when populations change as they adapt to different environmental conditions.  Convergent evolution Two unrelated species develop similar traits after developing independently in similar environmental conditions.

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Phylogenetic Tree shows Divergence

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Co-evolution  Coevolution occurs when organisms are linked with other organisms and gradually evolve together.Predators and prey, pollinators and plants, and parasites and hosts all influence each others evolution.  Many plants rely on insects and birds to spread their pollen, this causes the plants to change themselves in ways that will entice these organisms to come to the plants.  Examples: The constant threat of predators can cause prey species to evolve faster legs, stronger shells, better camouflage, more effective poisons, etc. The struggle between parasites and hosts is another example of coevolution. Parasites such as bacteria, protozoa, fungi, algae, plants and animals consume their host in order to survive. Thus, the hosts must develop ways to defend themselves against the predator.

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Co-evolution Examples

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Pace of Evolution  Two models attempt to explain the rate of evolutionary change Gradualism  change occurs within a particular lineage at a slow and steady pace. According to this model, big changes occur from the accumulation of many small changes. Punctuated equilibrium  evolutionary change consists of long periods of stasis (equilibrium) or no change interrupted by periods of rapid divergence or change.